1. Field of the Invention
This invention relates to a liquid nebulizer which uses ultrasonic waves, and more particularly to an oscillator-exciting system for an ultrasonic liquid nebulizer.
2. Description of the Prior Art
When ultrasonic waves are generated in a liquid and directed to the top surface of the liquid, one or more liquid columns are formed on the top surface, and the liquid is nebulized into a mist-like state from the liquid column. This phenomenon is known, for instance, as disclosed in U.S. Pat. No. 3,387,607, and the phenomenon is used in medical instruments and in room humidifiers. With a conventional liquid nebulizer, a piezo-oscillator element is used for generating the ultrasonic waves, and the piezo-oxcillator element is excited by the output from a separate electric oscillating circuit whose oscillating frequency is determined solely by the constants of various electric parts within the oscillating circuit. The power from the oscillating circuit may be amplified before being applied to the piezo-oscillating element. In such a conventional oscillator-exciting system. the oscillating frequency of the separate oscillating circuit must be adjusted to the optimal frequency of the piezo-oscillator element or, if such adjustment is not possible, a piezo-oscillator element having an optimal frequency which is identical with the output frequency of the separate oscillating circuit must be selected. When the piezo-oscillator element is replaced due to failure or at the end of its service life, the aforesaid adjustment or the selection must be conducted for each replacement. Furthermore, in order to maintain the oscillating frequency at the optimal value regardless of the ambient temperature variation and power source voltage fluctuation, the separate oscillating circuit becomes complicated and expensive.
Therefore, an object of the present invention is to mitigate the aforesaid difficulties of the conventional ultrasonic liquid nebulizer, by providing an improved oscillator-exciting system for an altrasonic liquid nebulizer which system is made of a simple electric circuit and is easy to adjust and maintain.
Another object of the present invention is to provide an oscillator-exciting system for an ultrasonic liquid nebulizer, which system is provided with protective means for ceasing the oscillation in case of exhaustion of the liquid being nebulized and/or in case of excessive overcurrent therethrough.